RESUMO
Smad7 is a negative regulator of TGFbeta superfamily signaling. Using a three-component triple transgenic system, expression of the inhibitory Smad7 was induced via doxycycline within the NCC lineages at pre- and post-migratory stages. Consistent with its role in negatively regulating both TGFbeta and BMP signaling in vitro, induction of Smad7 within the NCC significantly suppressed phosphorylation levels of both Smad1/5/8 and Smad2/3 in vivo, resulting in subsequent loss of NCC-derived craniofacial, pharyngeal and cardiac OFT cushion cells. At the cellular level, increased cell death was observed in pharyngeal arches. However, cell proliferation and NCC-derived smooth muscle differentiation were unaltered. NCC lineage mapping demonstrated that cardiac NCC emigration and initial migration were not affected, but subsequent colonization of the OFT was significantly reduced. Induction of Smad7 in post-migratory NCC resulted in interventricular septal chamber septation defects, suggesting that TGFbeta superfamily signaling is also essential for cardiac NCC at post-migratory stages to govern normal cardiac development. Taken together, the data illustrate that tightly regulated TGFbeta superfamily signaling plays an essential role during craniofacial and cardiac NCC colonization and cell survival in vivo.
Assuntos
Regulação da Expressão Gênica , Crista Neural/metabolismo , Proteína Smad7/genética , Proteína Smad7/fisiologia , Animais , Região Branquial/anormalidades , Doenças Cardiovasculares/congênito , Doenças Cardiovasculares/genética , Linhagem da Célula , Sobrevivência Celular , Anormalidades Craniofaciais/genética , Camundongos , Modelos Biológicos , Modelos Genéticos , Miocárdio/metabolismo , Ativação Transcricional , TransgenesRESUMO
Smad7 can be induced by various transforming growth factor-beta superfamily ligands and negatively modulates their signaling, thus acting in a negative, autocrine feedback manner. Previous analyses have demonstrated that although Smad7 is widely expressed, it is predominantly found in the vascular endothelium. Because of the restricted spatiotemporal reporter expression driven via a novel 4.3 kb Smad7 promoter in endocardial cells overlying the hearts atrioventricular (AV) cushions; we hypothesized that a transgenic Cre line would prove useful for the analysis of endocardial cushion and valve formation. Here we describe a mouse line, Smad7(Cre), where Cre is robustly expressed within both cardiac outflow and AV endocardial cushions. Additionally, as endocardial cells are thought to contribute at least in part to the formation of the endocardial cushion mesenchyme, we crossed the Smad7(Cre) mice to the ROSA26(eGFP-DTA) diphtheria toxin A-expressing mice in order to genetically ablate Smad7(Cre) expressing cells. Ablation of Smad7(Cre) cells resulted in embryonic lethality by E11.5 and largely acellular endocardial cushions.